Power tool with step-up converter

ABSTRACT

A power tool, includes an electrical motor unit connectable to a battery unit, wherein: a step-up converter, connectable between the battery unit and electrical motor unit, converts a battery voltage U battery  provided by the battery unit to a higher step-up voltage U step-up , and provides U step-up  to the electrical motor unit as an output voltage U output ; a bypass circuit, arranged in parallel with the step-up converter, connects the battery unit to and provides U battery  to the electrical motor unit as U output ; and at least one control unit is arranged to control the step-up converter and the bypass circuit, such that U output  can switch between U battery  and U step-up , based on tool related parameters, including U output , an output current I output  provided to the motor, a rotational speed ω motor  of the motor unit multiplied with a torque T provided by the tool, and an output power P output  provided to the electrical motor unit.

FIELD OF THE INVENTION

The present invention relates to a power tool including an electricalmotor unit that is connectable to a battery unit.

The present invention also relates to a method for providing anelectrical motor unit of a power tool with an output voltage U_(output).

The present invention also relates to a computer program and to acomputer program product.

RELATED ART AND BACKGROUND OF THE INVENTION

Power tools including an electrical motor unit are often provided withelectrical power from a battery unit. FIG. 1 schematically shows anexample of such a power tool 100. The power tool 100 includes abody/housing 101 and a shaft/spindle 102. An electrical motor unit isused for driving the shaft 102. The electrical motor is driven by abattery unit 104. The battery unit 104 can be mounted at a handle 103 ofthe power tool, as shown in FIG. 1, but can also be mounted on otherparts of the power tool 100. However, the battery unit 104 can also belocated separated from the power tool 100, and the electrical power canthen be provided to the electrical motor unit by one or more cables thatare connected between the external battery unit and the power tool 100.The power tool 100 further includes a number of parts not shown in FIG.1, as is understood by a skilled person.

Power tools of today, such as nut-runners, generally have problemsrelating to the size and weight of the power tool. There is generally ademand for reducing the size and/or the weight of the power tools, sincea small and lightweight power tool is very useful for the consumer,because it is easy to transport and also practical to use, since it isnot too heavy to hold and handle.

Power tools include a number of parts adding to the size and/or weightof the tool. One part having a big influence on the both the size andthe weight of the tool is the battery unit. The performance of the powertool is today directly related to the power being supplied by thebattery unit, and is thereby also directly related to the size andweight of the battery unit. For example, both the run-down speed and thetorque provided by a nut-runner are directly related to a voltage levelof the battery unit. Therefore an efficient and high performingnut-runner today has to be provided with a large and heavy battery pack.

In order to try to adapt the power tool to a current performance demand,while minimizing the size and/or weight of the tool, some prior artsolutions have utilized a set of different battery units or batterieshaving different powers and/or voltages. Thus, depending on the neededperformance of the power tool, the user has the possibility to choose asuitable battery unit or battery from this set to be connected to thepower tool. Hereby, the size and weight of the power tool can be adaptedto the performance demand. Handling of a very powerful power tool, whichalso is very heavy and large, when a much less powerful, and also muchsmaller and lighter, tool would have been sufficient can hereby beavoided.

However, the set of battery units that can be used in the power toolmust still be carried along with the power tool by a user to achieveadaptability of performance and size of the tool. Also, all batteryunits have to be charged for the user to be able to adapt the batterysupply during work with the tool, which makes this solution not verypractical. Also, battery units and/or batteries having different powersand/or voltages are today often provided with different connectioninterfaces. Thus, a first battery having a first voltage/power may bedirectly connectable to the power tool while a second battery having asecond voltage/power is often not directly connectable to the powertool. It might therefore be difficult to efficiently interchange thebatteries, at least without the use of one or more battery adapters.

AIM AND MOST IMPORTANT FEATURES OF THE INVENTION

It is an object of the present invention to provide a power tool that atleast partly solves one or more of the above stated problems.

The present invention aims to provide a more compact and lightweightpower tool than the power tools known in the background art.

The power tool and method according to the present invention arecharacterized in that an output voltage U_(output) that is provided toan electrical motor unit in the tool may be switched between a batteryvoltage U_(battery) and a higher step-up voltage U_(step-up). Thisswitchable output voltage U_(output) is according to the claimedinvention achieved by a step-up converter, a bypass circuit, and atleast one control unit controlling the step-up converter and the bypasscircuit.

The step-up converter is connectable between a battery unit and theelectrical motor unit and is arranged for converting, when enabled, abattery voltage U_(battery) being provided to the step-up converter bythe battery unit to a higher step-up voltage U_(step-up);U_(step-up)>U_(battery). This step-up voltage U_(step-up) is thenprovided to the electrical motor unit as an output voltage U_(output);U_(output)=U_(step-up).

The bypass circuit is arranged in parallel with the step-up converter,thereby connecting, when enabled, the battery unit directly to theelectrical motor unit and providing the battery voltage U_(battery) tothe electrical motor unit as an output voltage U_(output);U_(output)=U_(battery).

At least one control unit is arranged for controlling the step-upconverter and the bypass circuit in order to switch the output voltageU_(output) between the battery voltage U_(battery) and the step-upvoltage U_(step-up). This controlled switching can be achieved bygenerating a bypass enabling/disabling signal S_(bypass_on/off) and astep-up enabling/disabling signal S_(step-up_on/off), and by provingthese enabling/disabling signals to the bypass circuit and the step-upconverter, respectively.

The power tool according to the present invention can utilizeenabling/disabling of the bypass circuit and the step-up converter,respectively, to alter the output voltage U_(output) that is provided tothe motor unit such that a temporally increased rotational speed of theelectrical motor unit is achieved. Hereby the productivity of the powertool is increased.

Alternatively, a smaller and lighter battery unit, and thereby a morecompact and less heavy power tool, as compared to prior art power tools,can be provided by the present invention. A compact and lightweightpower tool is easily handled and therefore the usage of the power toolis improved by the present invention.

According to an embodiment of the present invention, the power tool canbe particularly adapted to perform certain activations of the tool, suchas tightening and/or loosening of nuts, during which the speed and/ortorque should change during the activation to achieve optimalperformance. For example, when tightening of a nut, the step-upconverter can be enabled and the bypass circuit can be disabled during afirst phase of the tool activation. During a second phase, the bypasscircuit can be enabled and the step-up converter can be disabled.Hereby, a high rotational speed and low torque is provided by the powertool during the first phase, followed by a lower rotational speed andhigher torque during the second phase. This gives an optimal performancefor e.g. a nut-runner when tightening a nut, where a high speed but nottoo much moment of force is needed during the first phase, and much moremoment of force is needed during the second phase. According to theinvention, this optimal performance is achievable with a compact andlightweight power tool.

When loosening a nut, the first phase can instead provide a high torqueT and low rotational speed, and the second phase can provide a highrotational speed and a low torque. This is achieved by enabling thebypass circuit and disabling the step-up converter during the firstphase of the activation, followed by enabling the step-up converter anddisabling the bypass circuit during the second phase. This gives anoptimal performance to e.g. a compact and lightweight nut-runner whenloosening a nut, where much rotational force is needed during the firstphase, and much less rotational force is needed during the second phase.

Detailed exemplary embodiments and advantages of the power tool and themethod according to the invention will now be described with referenceto the appended drawings illustrating some preferred embodiments.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a power tool. FIG. 2 shows a power tool according to thepresent invention.

FIG. 3 shows a power tool according to the present invention.

FIG. 4 shows a tool activation diagram for a tool according to anembodiment of the invention.

FIG. 5 shows a flowchart of an activation method for a tool according toan embodiment of the invention.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

According to the present invention, the power tool includes a step-upconverter, a bypass circuit, and at least one control unit as will beexplained in detail below. FIG. 2 schematically shows such a power tool200. In FIG. 2, the step-up converter, the bypass circuit, and the oneor more control units are illustrated as a step-up/bypass module 202being connectable between a battery unit 204 and an electrical motorunit 203 located within the body 201 of the tool 200.

According to one embodiment of the invention, the step-up module 202,i.e. the step-up converter, the bypass circuit, and the one or morecontrol units, is arranged integrated within the body 201 of the powertool 200, and is connected to the electrical motor unit 203 and to thebattery unit 204.

According to another embodiment of the invention, the step-up/bypassmodule 202 is integrated with the battery unit 204. Here the integratedbattery and step-up/bypass module 202, 204 is connectable to the motorunit 203 of the tool 200.

According to another embodiment of the invention, the step-up/bypassmodule 202 is arranged separately, i.e. as a separate unit, between thebattery unit 204 and the motor unit 203. The separately arrangedstep-up/bypass module 202 is here thus connectable to both the batteryunit 204 and to the motor unit 203.

FIG. 3 schematically shows a power tool 300 according to the presentinvention. In FIG. 3, the power tool 300 is schematically illustrated asincluding the battery unit 304 and the step-up/bypass module 302.However, as stated above, the battery unit 304 and/or the step-up/bypassunit 302 and/or the one or more control units 331, 332 can also bearranged separately from the power tool 300, i.e. external from the bodyof the power tool.

The power tool 300 includes an electrical motor unit 303, which isconnectable to the battery unit 304 via the step-up/bypass module 302.In FIG. 3, an inverter 305 is included in the electrical motor unit 303.However, depending on the construction of the electrical motor unit 303and/or of the step-up/bypass module 302, the inverter 305 may be omittedin the power tool 300.

The step-up/bypass module 302 includes a step-up converter 310 and abypass circuit 320. The step-up converter 310 is connectable between thebattery unit 304 and the electrical motor unit 303. The step-upconverter 310 can be enabled and disabled, and is arranged forconverting, when enabled, a battery voltage U_(battery) being providedto the step-up converter 310 by the battery unit 304. The step-upconverter 310 thereby converts the battery voltage U_(battery) to ahigher step-up voltage U_(step-up); U_(step-up)>U_(battery). This higherstep-up voltage U_(step-up) is then provided to the electrical motorunit 303 as an output voltage U_(output) on the output DC bus 325, i.e.U_(output)=U_(step-up). Thus, the electrical motor unit 303 is providedwith the higher step-up voltage U_(step-up) when the step-up converter310 is enabled.

The bypass circuit 320 is arranged in parallel with the step-upconverter 310, and is thus also connectable between the battery unit 304and the electrical motor unit 303. When the bypass circuit 320 isenabled, the battery unit 304 is connected to the electrical motor unit303 through the bypass circuit 320. The bypass circuit is thus arrangedfor providing the battery voltage U_(battery) to the electrical motorunit 303, as an output voltage U_(output) on the output DC bus 325, i.e.U_(output)=U_(battery).

The power tool can also be equipped with a brake chopper arranged forprotecting the battery unit 304 by preventing the output voltageU_(output) on the output DC bus 325 to reach too high levels when theelectrical motor unit 303 is braked/decelerated. Generally, energy iscreated by the electrical motor unit 303 when a user lets go of the tooltrigger, whereby the rotational speed of the power tool is reduced,especially if the higher step-up voltage U_(step-up) has been providedto the electrical motor unit before braking the electrical motor unit isinitiated. The brake chopper can be arranged at the output DC bus 325,between the step-up/bypass module 302 and the electrical motor unit 303.For example, the brake chopper can be implemented as a resistancecoupled in series with a switch, such as a MOSFET (Metal OxideSemiconductor Field Effect Transistor), over the output DC bus 325, andwith a diode coupled in parallel with the resistance. Hereby, the energythat is created by the electrical motor unit 303 during its decelerationcan be consumed by the resistance, which reduces the output voltageU_(output) on the output DC bus 325 in order to protect the battery unit304.

The power tool 300 according to the present invention further includesat least one control unit 331, 332. The at least one control unit 331,332 is arranged for controlling the step-up converter 310 and the bypasscircuit 320 by enabling/disabling the step-up converter 310 and thebypass circuit 320. The output voltage U_(output) on the output DC bus325 may hereby be switched between the battery voltage U_(battery) andthe step-up voltage U_(step-up). Thus, by controlling theenabling/disabling of the step-up converter 310 and the bypass circuit320, respectively, the output voltage U_(output) on the output DC bus325 can be toggled between the lower battery voltage U_(battery) and thehigher step-up voltage U_(step-up); U_(battery)≤U_(output)≤U_(step-up).

The power tool 300 according to the present invention can thustemporally increase the rotational speed of the electrical motor unit303 by providing the temporally increased step-up voltage U_(step-up) tothe electrical motor unit 303. Hereby the productivity of the power tool300 is increased.

Alternatively, the same rotational motor speed as was used in prior artsolutions can be achieved by use of a battery unit having a lowervoltage U_(battery_invention) than was possible for the battery voltageU_(battery_prior art) in the prior art solutions;U_(battery_invention)<U_(battery_prior art); since the increased step-upvoltage U_(step-up) by the invention temporally can be high enough tomatch the prior art voltage U_(step-up)=U_(battery_prior art). Hereby asmaller and lighter battery unit 304, and thereby a more compact andless heavy power tool 300, is provided by the present invention. Acompact and lightweight power tool 300 is easily handled, and thereforeeasier more attractive usage of the power tool 300 is facilitated by theinvention.

Also, the step-up and bypass module 302 can be made compact andlightweight according to the solution of the present invention. This isdue to the use of the bypass circuit 320 according to the invention.When the motor 303 provides a high effect during heavy load, the bypasscircuit 320 is enabled and the step-up converter 310 is disabled,whereby the battery unit 304 is directly coupled to the motor unit 303,possibly including an inverter 305. Hereby, the components of thestep-up converter 310 only have to be able to cope with a limited power,since the step-up converter 310 is bypassed when a maximum power isprovided from the battery unit 304 to the motor unit 303. Thus, sincethese components only have to cope with a relatively low electricalpower, the step-up and bypass module 302 can be designed to be compactand lightweight, which also reduces the total size and weight of thepower tool 300.

According to an embodiment of the present invention, the step-upconverter 310 is a synchronous step-up converter, which is arranged forcreating the higher step-up voltage U_(step-up), said step-up converterincluding at least one step-up transistor 311, at least one inductor313, and at least one step-up switch 312. The at least one step-uptransistor 311 and/or the at least one step-up switch 312 can typicallybe switched at a relatively high frequency, e.g. at a frequency in thekilohertz (kHz) range. As illustrated in FIG. 3, the inductor 313 iscoupled in series with the battery unit 304 and the step-up switch 312.The step-up transistor 311 is coupled in parallel with the battery unit304 and in parallel with an output capacitor 314 that is coupled overthe output DC bus 325.

The step-up converter can further include a step-up control circuitrybeing arranged for controlling the at least one step-up transistor 311and/or the at least one step-up switch 312, where the step-up switch 312can be used for connecting the step-up converter 310 to the output DCbus 325, i.e. to the electrical motor unit 303, when enabled. Thestep-up control circuitry includes a voltage regulation circuitry 316and a PWM (Pulse Width Modulation) circuit 317. The voltage regulationcircuitry 316, which can be implemented as an amplifier, is arranged forcontrolling the level of the higher step-up voltage U_(step-up) towardsits target voltage U_(target) by controlling the PWM circuit 317. Thevoltage regulation circuitry 316 has the output DC bus 325 as an input315.

The PWM circuit 317 also includes an overload limiting function, whichlimits/reduces the step-up voltage U_(step-up) if the step-up converter310 is overloaded. The PWM circuit 317 also has an input receiving acontrol signal S_(step-up_on/off) being provided from a control unit 332as an input signal. The function of the at least one step-up transistor311 and the at least one step-up switch 312 is thus controlled by thestep-up control circuitry, and in particular by the PWM circuit 317. Thecontrol signal that is used for controlling the step-up transistor 311is provided directly by the PWM circuit 317. The control signal that isused for controlling the step-up switch 312 is an amplified and invertedversion of the control signal provided by the PWM circuit 317, where theamplification and inversion are performed by the amplifier/inverter 318.

According to an embodiment of the present invention, the bypass circuit320 includes a bypass switch 321, which is controllable by a controlunit 331 providing a bypass control signal S_(bypass_on/off). Thus, thebypass switch 321 is switched at a very low frequency, e.g. twice peractivation of the tool, as will be described more in detail below. Anamplifier 322 can be used for amplifying the bypass control signalS_(bypass_on/off) from the control unit 331 before providing theamplified control signal to the bypass switch 321.

In FIG. 3, for illustrative reasons, the control units 331, 332providing the control signals S_(bypass_on/off) and S_(step-up_on/off)are illustrated as two separate control units. However, as is clear fora skilled person, both of these control signals S_(bypass_on/off) andS_(step-up_on/off) can also be provided by a single control unit,essentially including the above and/or below described functions of bothof these control units 331, 332.

According to an embodiment of the present invention, one or more of theat least one step-up switch 311, the step-up switch 312, and the atleast one bypass switch 321 are implemented as an N-channel MOSFET(Metal Oxide Semiconductor Field Effect Transistor), an P-channel MOSFET(Metal Oxide Semiconductor Field Effect Transistor), or another suitablecontrollable switching device.

According to an embodiment of the present invention, at least one of thestep-up switch 312 and the at least one bypass switch 321 areimplemented as power diodes, which are especially suitable for lowerpower applications.

According to an embodiment of the present invention, the step-upconverter 310 is a multi-phase converter that is adapted to convert thebattery voltage U_(battery) to a higher step-up voltage U_(step-up). Themulti-phase converter can be a boost type converter, being controllableby the control signal S_(step-up_on/off).

According to an embodiment, the step-up converter 310 is implemented asincluding two step-up transistor circuits that is operated in mutuallyopposite phases. Hereby, a smooth output step-up voltage U_(step-up) canbe provided by the step-up converter 310, since a voltage/current rippleon the output DC bus 325 can be reduced by the opposite phase coupledtransistor configuration.

According to an embodiment of the invention, the battery unit 304includes at least one super capacitor. Super capacitors have a very highcapacitance value per unit volume and a very high energy density. Thesuper capacitors can thus be utilized as a reliable energy source, as analternative to a conventional battery. The super capacitors are alsovery lightweight, much lighter than a corresponding conventional batteryenergy source. One problem with super capacitors is that they lose theirpower after a while. However, it is possible to very quickly rechargethem again. By the use of the present invention, the output voltage ofthe super capacitor can be boosted when needed, e.g. when the supercapacitor has lost some of its power. For example, the power toolaccording to the invention, e.g. including a super capacitor in thebattery unit, can be used in an assembly line, where the tool could beused for sequential relatively short time periods and could be rechargedbetween these short time periods. By the use of super capacitors, a verycompact and light power tool can be provided by implementation of thepresent invention.

Thus, the at least one control unit 331, 332 is, according to theinvention, arranged for providing the bypass circuit 320 with a bypassenabling/disabling signal S_(bypass_on/off). The bypass circuit 320 isarranged for enabling/disabling the bypass, i.e. forconnecting/disconnecting the battery unit 304 to the electrical motorunit 303 based on the bypass enabling/disabling signalS_(bypass_on/off).

Correspondingly, the at least one control unit 331, 332 is arranged forproviding the step-up converter 310 with a step-up enabling/disablingsignal S_(step-up_on/off). Here, the step-up converter 310 is arrangedfor enabling/disabling the voltage conversion of the step-up converter310 based on that step-up enabling/disabling signal S_(step-up_on/off).

According to an embodiment of the present invention, the bypassenabling/disabling signal S_(bypass_on/off) and the step-upenabling/disabling signal S_(step-up_on/off) are complementary signals.Thus, the bypass enabling/disabling signal S_(bypass_on/off) and thestep-up enabling/disabling signal S_(step-up_on/off) have inversevalues. In other words, the bypass enabling/disabling signalS_(bypass_on/off)is an inverse/negated version of the step-upenabling/disabling signal S_(step-up_on/off).

Thus, the at least one control unit 331,332 can preferably be utilizedfor toggling the output DC bus 325 between the battery voltageU_(battery) and the higher step-up voltage U_(step-up), therebyproviding a power tool 300 having the above mentioned advantages of thepresent invention. A compact and lightweight power tool having highproductivity is thus provided by the invention.

As described above, the voltage on the output DC bus 325 can be switchedbetween the battery voltage U_(battery) and the higher step-up voltageU_(step-up) based on an step-up enabling/disabling signalS_(step-up_on/off) that is provided to the PWM circuit 317 by the atleast one control unit 331, 332 and/or based on a bypassenabling/disabling signal S_(bypass_on/off) that is provided to thebypass switch 321 by the at least one control unit 331, 332.

The step-up enabling/disabling signals S_(step-up_on/off) and the bypassenabling/disabling signals S_(bypass_on/off) are thus created in the atleast one control unit 331, 332. The form of these step-upenabling/disabling signals S_(step-up_on/off) and bypassenabling/disabling signals S_(bypass_on/off) can be determined by the atleast one control unit based on a number of different parameters, eitherbased on single parameter values taken alone, or on two or moreparameters in combination.

According to an embodiment of the invention, the at least one controlunit is arranged to base the step-up S_(step-up_on/off) and/or bypassS_(bypass_on/off) enabling/disabling signals on a relation between theoutput voltage U_(output) on the output DC bus 325 and a voltagethreshold U_(threshold). Here, a step-up enabling signal S_(step-up_on)and a bypass disabling signal S_(bypass_off) are generated by the atleast one control unit 331, 332 when the output voltage U_(output) isequal to or higher than the voltage threshold U_(threshold);U_(output)≥U_(threshold). The embodiment is described more in detailbelow.

According to another embodiment of the invention, the at least onecontrol unit 331, 332 is arranged to base the step-up S_(step-up_on/off)and/or S_(bypass_on/off) bypass enabling/disabling signals on a relationbetween an output current I_(output) that is provided to the motor unit303 on the output DC bus 325 and a current threshold I_(threshold).Here, a step-up disabling signal S_(step-up_off) and a bypass enablingsignal S_(bypass_on) are generated by the at least one control unit 331,332 when the output current I_(output) is equal to or higher than thecurrent threshold I_(threshold); I_(output)≥I_(threshold). Theembodiment is described more in detail below.

According to an embodiment of the invention, the at least one controlunit 331, 332 is arranged to base the step-up S_(step-up_on/off) and/orbypass S_(bypass_on/off) enabling/disabling signals on a relationbetween a rotational speed ω_(motor) of the motor unit 303 multipliedwith a torque T that is provided by the tool 300; ω_(motor)*T; and aspeed and torque threshold ωT_(threshold). Thus, the rotational speedω_(motor) and the torque T that is provided by the shaft/spindle 102 ofthe power tool is here compared with the speed and torque thresholdωT_(threshold). A step-up enabling signal S_(step-up_on) and a bypassdisabling signal S_(bypass_off) is according to the embodiment generatedby the at least one control unit 331, 332 when the rotational speedω_(motor) multiplied with the torque T; ω_(motor)*T; is lower than thespeed and torque threshold ωT_(threshold); ω_(motor)*T<ωT_(threshold).The embodiment is described more in detail below.

According to an embodiment of the invention, the at least one controlunit 331, 332 is arranged to base the step-up S_(step-up_on/off) and/orbypass S_(bypass_on/off) enabling/disabling signals on a relationbetween an output power P_(output) that is provided to the electricalmotor unit 303 on the output DC bus 325 and a power thresholdP_(threshold). Here, a step-up enabling signal S_(step-up_on) and abypass disabling signal S_(bypass_off) are generated by the at least onecontrol unit 331, 332 when the output power P_(output) on the output DCbus 325 is lower than the power threshold P_(threshold);P_(output)<P_(threshold). The embodiment is described more in detailbelow.

According to an aspect of the present invention, a method for providingan electrical motor unit 304 of a power tool 300 with an output voltageU_(output) is presented. According to the method, at least one controlunit 331, 332 is used for controlling the step-up converter 310 and thebypass circuit 320, as described above, such that the output voltageU_(output) on the output DC bus 325 may be switched between the batteryvoltage U_(battery) and the step-up voltage U_(step-up);U_(battery)≤U_(output)≤U_(step-up). This toggling output voltage isachieved by converting, when the step-up converter 310 is enabled, thebattery voltage U_(battery) that is provided to the step-up converter310 by the battery unit 304 to the higher step-up voltage U_(step-up);U_(step-up)>U_(battery). This step-up voltage U_(step-up) is thenprovided to the electrical motor unit 303 as an output voltageU_(output); U_(output)=U_(step-up). The toggling output voltage is alsoachieved by connecting, when the bypass circuit 320 is enabled, thebattery unit 304 to the electrical motor unit 303, whereby the batteryvoltage U_(battery) is provided to the electrical motor unit 303 as anoutput voltage U_(output); U_(output)=U_(battery).

By use of the method according to the present invention, the power tool300 can be made compact in size and light in weight at the same time asit is possible to provide a high productivity when using the tool.

The at least one control unit 331, 332 thus controls the output voltageU_(output) on the output DC bus 325 to switch between the batteryvoltage U_(battery) and the step-up voltage U_(step-up);U_(battery)≤U_(output)≤U_(step-up). The at least one control unit candetermine the suitable output voltage U_(output) based on a number ofparameters.

One such parameter is the level of the output voltage U_(output) itself,whereby the at least one control unit 331, 332 disables the step-upconverter 310 and enables the bypass circuit 320 when the output voltageU_(output) is lower than a voltage threshold U_(threshold);U_(output)<U_(threshold). As described above, the PWM circuit 317 caninclude an overload limiting function, which reduces the step-up voltageU_(step-up) if the step-up converter 310 is overloaded. Thus, also lowoutput voltage values; U_(output)<U_(threshold); resulting from suchstep-up converter overload and the following step-up voltage U_(step-up)reduction, can be utilized as a parameter to base control of the step-upconverter 310 and/or bypass circuit 320 on.

Another such parameter is the output current I_(output), whereby the atleast one control unit 331, 332 disables the step-up converter 310 andenables the bypass circuit 320 when the output current I_(output) ishigher than or equal to a current threshold I_(threshold);I_(output)≥I_(threshold). The output current I_(output) can here (and intable 1 below) either correspond to the current on the output DC bus325, or to a motor current I_(motor), that is provided to, and measuredat, the motor, i.e. between the inverter 305 and the motor. The motorcurrent I_(motor) is normally already measured in power tools of today.Therefore, it adds very little complexity to use the motor currentI_(motor) as the output current I_(output) parameter, since thisparameter is output today already available in power tools.

The motor current I_(motor) and the current on the output DC bus 325 candiffer, since the motor current I_(motor) is dependent on the torque Tthat is provided by the tool, whereas the current on the output DC bus325 is dependent on the electrical power that is provided to theinverter 305.

Some examples of the parameters and the conditions for theenabling/disabling signals for the step-up converter S_(step-up_on/off)and/or for the bypass circuit S_(bypass_on/off) based on differentvalues for these parameters are shown in table 1.

In tables 1, 2 and 3 below, and in this document, S_(bypass_on/off)=1means that the bypass circuit 320 is enabled (S_(bypass_on)) andS_(bypass_on/off)=0 means that the bypass circuit 320 is disabled(S_(bypass_off)). Correspondingly, S_(step-up_on/off)=1 means that thestep-up converter 310 is enabled (S_(step-up_on)) andS_(step-up_on/off)=0 means that the step-up converter 310 is disabled(S_(step-up_off)). Also, the tool trigger signal has the value 1 whenthe tool motor unit 303 is running and the value 0 when the motor unit303 is not running. Thus, tool trigger=0 means that the motor unit isoff and tool trigger=1 means that the motor unit is on/activated.

TABLE 1 S_(bypass) _(—) _(on/off) S_(step-up) _(—) _(on/off) U_(output)I_(output) Tool trigger 0 1 U_(output) ≥ I_(output) < 1 U_(threshold)I_(threshold) 1 0 U_(output) < I_(output) < 1 U_(threshold)I_(threshold) 1 0 U_(output) > I_(output) ≥ 1 U_(threshold)I_(threshold) 1 0 U_(output) < I_(output) ≥ 1 U_(threshold)I_(threshold) 1 0 Ignored Ignored 0

The U_(output) and I_(output) values in the tables correspond to thevoltage and current values on the output DC bus 325. Alternatively, theI_(output) values may correspond to the above mentioned motor currentI_(motor), as described above. As can be seen in table 1, one or more ofthese values U_(output), I_(output) can e.g. be used as conditions fortriggering the one or more control units 331, 332 to enable the bypasscircuit S_(bypass_on) and to disable the step-up converterS_(step-up_off) when the output voltage U_(output) on the DC-bus 325drops below a preset value U_(threshold) while the tool trigger is incondition on, i.e. when the tool 300 is activated. Also, the one or morecontrol units 331, 332 can be triggered to enable the bypass circuitS_(bypass_on) and disable the step-up converter S_(step-up_off) when theoutput current I_(output) on the DC-bus 325 is higher than or equal to apreset value I_(threshold) while the tool trigger is in condition on.

Another such parameter is the rotational speed ω_(motor) and torque Tthat is provided by the power tool 300, whereby the at least one controlunit 331, 332 enables the step-up converter 310 and disables the bypasscircuit 320 when the rotational speed ω_(motor) of the motor unit 303multiplied with a torque T that is provided by the power tool 300;ω_(motor)*T; is lower than the speed and torque thresholdωT_(threshold); ω_(motor)*T<ωT_(threshold).

Examples of the parameters and the conditions for the enabling/disablingsignals for the step-up converter S_(step-up_off) and/or for the bypasscircuit S_(bypass_off) on/off based on different values for thisparameter are shown in table 2.

TABLE 2 S_(bypass) _(—) _(on/off) S_(step-up) _(—) _(on/off) ω_(motor)*TTool trigger 0 1 ω*T < ωT_(threshold) 1 1 0 ω*T ≥ ωT_(threshold) 1 1 0Ignored 0

In table 2, ω is the rotational speed of the tool in rad/s and T is thetorque in Nm that is provided by the tool.

As can be seen in table 2, the parameter values for ω_(motor)*T can beused as conditions for triggering the one or more control units 331, 332to enable the bypass circuit S_(bypass_on) and to disable the step-upconverter S_(step-up_off) when ω*T≥ωT_(threshold) while the tool triggeris in condition on, i.e. when the tool 300 is activated. Also, the oneor more control units 331, 332 can be triggered to disable the bypasscircuit S_(bypass_off) and enable the step-up converter S_(step-up_on)when ω*T<ωT_(threshold) while the tool trigger is in condition on.

Another such parameter is the output power P_(output) on the output DCbus 325, whereby the at least one control unit 331, 332 enables thestep-up converter 310 and disables the bypass circuit 320 when theoutput power P_(output) that is provided to said electrical motor unit303 is lower than a power threshold P_(threshold);P_(output)<P_(threshold).

Examples of the parameters and the conditions for the enabling/disablingsignals for the step-up converter S_(step-up_on/off) and/or for thebypass circuit S_(bypass_on/off) based on different values for thisparameter are shown in table 3.

TABLE 3 S_(bypass) _(—) _(on/off) S_(step-up) _(—) _(on/off) P_(output)Tool trigger 0 1 P_(output) < P_(threshold) 1 1 0 P_(output) ≥P_(threshold) 1 1 0 Ignored 0

Here, the output power P_(output) on the output DC bus 325 can becalculated as P_(output)=I_(output)*U_(output) on the output DC bus 325.

As can be seen in table 3, the parameter values for the output powerP_(output) can be used as conditions for triggering the one or morecontrol units 331, 332 to enable the bypass circuit S_(bypass_on) and todisable the step-up converter S_(step-up_off) when P_(output)≥P_(threshold) while the tool trigger is in condition on. Also, the oneor more control units 331, 332 can be triggered to disable the bypasscircuit S_(bypass_off) and enable the step-up converter S_(step-up_on)when P_(output)<P_(threshold) while the tool trigger is in condition on.

According to an embodiment, the at least one control unit 331, 332 canbase the enabling/disabling signals for the step-up converterS_(step-up_on/off) and/or for the bypass circuit S_(bypass_on/off) on acombination of two or more of these parameters, i.e. on two or more ofthe output voltage U_(output), the output current I_(output), therotational speed ω_(motor) and torque T, and the output powerP_(output).

FIG. 4 schematically illustrates a non-limiting example describing apossible use of the present invention, which could correspond e.g. to atool use including tightening of a nut. FIG. 5 shows a flow sheetdiagram for the corresponding method according to an embodiment of theinvention.

In a first step 501 of the method, the power tool 300 is activated, i.e.the tool trigger has the value 1. In FIG. 4, this happens at theposition “Tool trigger” along the time axis.

In a second step 502, the step-up converter 310 is enabledS_(step-up_on/off)=1 and the bypass circuit 320 is disabledS_(bypass_on/off)=0. The first phase of the tool activation is therebystarted, wherein the higher step-up voltage U_(step-up) is provided tothe electrical motor unit 303 as an output voltage U_(output) on theoutput DC bus 325 (curve 2 in FIG. 4); U_(output)=U_(step-up). Hereby,the rotational speed ω_(motor) of the motor unit 303 is increased (curve1 in FIG. 4) as a result of the higher step-up voltage U_(step-up) thatis input to the motor unit 303. Also, the output current I_(output)and/or the torque T (curve 3 in FIG. 4) is slightly increased. Thus,during the first phase, where the step-up converter is enabled/turnedon, an increased rotational speed ω_(motor) can be achieved by thepresent invention, which means that the nut can be quickly tightenedduring a phase where not too much torque is needed for the tightening.

In a third step 503, the bypass circuit 320 is enabledS_(bypass_on/off)=1 and the step-up converter 310 is disabledS_(step-up_on/off)=0 during the second phase of the activation. Thebattery voltage U_(battery) is thereby provided to the electrical motorunit 303 as an output voltage U_(output) (curve 2 in FIG. 4);U_(output)=U_(battery). Hereby, the rotational speed ω_(motor) of themotor unit 303 is decreased (curve 1 in FIG. 4) as a result of the lowerbattery voltage U_(battery) that is input to the motor unit 303, andalso due to the increased resistance of the nut because of the highertorque needed. Also, the output current I_(output) and/or the torque T(curve 3 in FIG. 4) is increased. Thus, during the second phase, wherethe bypass circuit is enabled, an increased torque can be achieved bythe present invention during the second phase where a high torque T isneeded for the tightening.

According to another embodiment of the present invention, the power tool300 is arranged for providing a high torque T during a first activationphase, and a high rotational speed ω_(motor) during a second activationphase. This embodiment can be particularly useful e.g. for loosening ofnuts, where a high torque T is needed for the first actual looseningphase and a high speed ω_(motor) and low torque T is needed for thesecond phase, when the nut is already loosened. This embodiment isachieved by enabling the bypass circuit 320 S_(bypass_on/off)=1 anddisabling the step-up converter 310 S_(step-up_on/off)=0 during thefirst phase of the activation. The battery voltage U_(battery) isthereby provided to the electrical motor unit 303 as an output voltageU_(output), whereby high torque T and low speed ω_(motor) is provided.

Thereafter, the step-up converter 310 is enabled S_(step-up_on/off)=1and the bypass circuit 320 is disabled S_(bypass_on/off)=0 during thesecond phase, whereby the higher step-up voltage U_(step-up) is providedto the electrical motor unit 303 as an output voltage U_(output) on theoutput DC bus 325. Thus, a low torque T and high speed ω_(motor) isprovided during the second phase.

According to another embodiment of the present invention, the bypasscircuit 320 is enabled and the step-up converter 310 is disabled duringretardation, i.e. deceleration, of the rotational speed of the powertool. Thus, when the rotational speed of the electrical motor unit 303is quickly slowing down, the electrical motor unit 303 is coupleddirectly to the battery unit 304 and not to the step-up converter 310.Hereby, the rotational energy of the electrical motor unit 303 and ofthe spindle/shaft 102, that is set free during the retardation, can beconverted to electrical energy and can be utilized for charging thebattery unit 304. For example, when the battery unit 304 includes one ormore super capacitors, the electrical energy that is extracted from therotational energy made free during the retardation can be used forcharging the super capacitors.

The power tool of the invention can be adapted to perform any of thesteps of the method of the invention. The different steps of the methodof the invention described above can be combined or performed in anysuitable order.

The method of the invention can implemented by a computer program,having code means, which when run in a computer causes the computer toexecute the steps of the method. The computer program is included in acomputer readable medium of a computer program product. The computerreadable medium may consist of essentially any memory, such as a ROM(Read-Only Memory), a PROM (Programmable Read-Only Memory), an EPROM(Erasable PROM), a Flash memory, an EEPROM (Electrically Erasable PROM),or a hard disk drive.

The power tool and the methods according to the invention may bemodified by those skilled in the art, as compared to the exemplaryembodiments described above.

As is obvious for a skilled person, a number of other implementations,modifications, variations and/or additions can be made to the abovedescribed exemplary embodiments. It is to be understood that theinvention includes all such other implementations, modifications,variations and/or additions which fall within the scope of the claims.

The invention claimed is:
 1. A power tool, comprising an electricalmotor unit that is connectable to a battery unit, wherein: a step-upconverter is connectable between said battery unit and said electricalmotor unit, which is arranged for converting, when enabled, a batteryvoltage U_(battery) that is provided to said step-up converter by saidbattery unit to a higher step-up voltage U_(step-up),U_(step-up)>U_(battery), said step-up voltage U_(step-up) being providedto said electrical motor unit as an output voltage U_(output),U_(output)=U_(step-up); a bypass circuit is arranged in parallel withsaid step-up converter and connects, when enabled, said battery unit tosaid electrical motor unit and provides said battery voltage U_(battery)to said electrical motor unit as said output voltage U_(output),U_(output)=U_(battery); at least one control unit is provided forcontrolling said step-up converter and said bypass circuit such thatsaid output voltage U_(output) is switchable between said batteryvoltage U_(battery) and said step-up voltage U_(step-up); said controlunit is configured to control said step-up converter and said bypasscircuit to alter said output voltage U_(output) that is provided to saidelectrical motor unit to achieve a higher rotational speed of saidelectrical motor unit and a lower torque provided by said power toolduring a first phase of a screw tightening process, followed by a lowerrotational speed of said electrical motor unit and a higher torqueprovided by said power tool during a second phase of the screwtightening process; and said control by the control unit is performedbased on at least one of a plurality of different tool relatedparameters, said parameters comprising (i) said output voltageU_(output), (ii) an output current I_(output) being provided to saidelectrical motor unit, (iii) said rotational speed ω_(motor) of saidelectrical motor unit multiplied with said torque T being provided bysaid tool, ω_(motor)*T, and (iv) an output power P_(output) beingprovided to said electrical motor unit.
 2. The power tool according toclaim 1, wherein said step-up converter is a synchronous step-upconverter including at least one step-up transistor, at least oneinductor, and at least one step-up switch.
 3. The power tool accordingto claim 2, wherein said step-up converter includes a step-up controlcircuitry configured to control said at least one step-up transistor andsaid at least one step-up switch connecting said step-up converter tosaid electrical motor unit when enabled.
 4. The power tool according toclaim 3, wherein said step-up control circuitry includes a voltageregulation circuitry configured to control said higher voltageU_(step-up) towards a target voltage U_(target) and having an output ofsaid step-up converter as an input.
 5. The power tool according to claim1, wherein said bypass circuit includes a bypass switch controlled bysaid at least one control unit.
 6. The power tool according to claim 3,wherein said bypass circuit includes a bypass switch controlled by saidat least one control unit; and wherein one or more of said at least onestep-up switch, said step-up transistor, and said bypass switch areimplemented as any one in the group of: an N-channel MOSFET (Metal OxideSemiconductor Field Effect Transistor); and an P-channel MOSFET (MetalOxide Semiconductor Field Effect Transistor).
 7. The power toolaccording to claim 1, wherein said at least one control unit isconfigured to provide said bypass circuit with a bypassenabling/disabling signal S_(bypass_on/off), said bypass circuit beingconfigured to enable or disable the connection of said battery unit tosaid electrical motor unit based on said bypass enabling/disablingsignal S_(bypass_on/off).
 8. The power tool according to claim 1,wherein said at least one control unit is configured to provide saidstep-up converter with a step-up enabling/disabling signalS_(step-up_on/off), said step-up converter being configured to enable ordisable the voltage conversion of said step-up converter based on saidstep-up enabling/disabling signal S_(step-up_on/off).
 9. The power toolaccording to claim 7, wherein said at least one control unit isconfigured to provide said step-up converter with a step-upenabling/disabling signal S_(step-up_on/off), said step-up converterbeing configured to enable or disable the voltage conversion of saidstep-up converter based on said step-up enabling/disabling signalS_(step-up_on/off); and wherein said at least one control unit isconfigured to base said step-up enabling/disabling signalS_(step-up_on/off) and/or said bypass enabling/disabling signalS_(bypass_on/off) on a relation between the at least one of saidparameters (U_(output), I_(output), ω_(motor)*T, P_(output)) and atleast one threshold value (U_(threshold), I_(threshold), ωT_(threshold),P_(threshold)) relating to the at least one of said parameters.
 10. Thepower tool according to claim 7, wherein said at least one control unitis configured to provide said step-up converter with a step-upenabling/disabling signal S_(step-up_on/off), said step-up converterbeing configured to enable or disable the voltage conversion of saidstep-up converter based on said step-up enabling/disabling signalS_(step-up_on/off); and wherein said at least one control unit isconfigured to base said step-up enabling/disabling signalS_(step-up_on/off) and/or said bypass enabling/disabling signalS_(bypass_on/off) on a relation between said output voltage U_(output)and a voltage threshold U_(threshold).
 11. The power tool according toclaim 10, wherein said at least one control unit is configured togenerate a step-up enabling signal S_(step-up_on) and a bypass disablingsignal S_(bypass_off) when said output voltage U_(output) is equal to orhigher than said voltage threshold U_(threshold)(U_(output)≥U_(threshold)).
 12. The power tool according to claim 7,wherein said at least one control unit is configured to provide saidstep-up converter with a step-up enabling/disabling signalS_(step-up_on/off), said step-up converter being configured to enable ordisable the voltage conversion of said step-up converter based on saidstep-up enabling/disabling signal S_(step-up_on/off); and wherein saidat least one control unit is configured to base said step-upenabling/disabling signal S_(step-up_on/off) and/or said bypassenabling/disabling signal S_(bypass_on/off) on a relation between saidoutput current I_(output) being provided to said electrical motor unitand a current threshold I_(threshold).
 13. The power tool according toclaim 12, wherein said at least one control unit is configured togenerate a step-up disabling signal S_(step-up_off) and a bypassenabling signal S_(bypass_on) when said output current I_(output) isequal to or higher than said current threshold I_(threshold)(I_(output)≥I_(threshold)).
 14. The power tool according to claim 7,wherein said at least one control unit is configured to provide saidstep-up converter with a step-up enabling/disabling signalS_(step-up_on/off), said step-up converter being configured to enable ordisable the voltage conversion of said step-up converter based on saidstep-up enabling/disabling signal S_(step-up_on/off); and wherein saidat least one control unit is configured to base said step-upenabling/disabling signal S_(step-up_on/off) and/or said bypassenabling/disabling signal S_(bypass_on/off) on a relation between saidrotational speed ω_(motor) of said electrical motor unit multiplied withsaid torque T being provided by said tool, ω_(motor)*T, and a speed andtorque threshold ωT_(threshold).
 15. The power tool according to claim14, wherein said at least one control unit is configured to generate astep-up enabling signal S_(step-up_on) and a bypass disabling signalS_(bypass_off) when said rotational speed ω_(motor) multiplied with saidtorque T, ω_(motor)*T, is lower than said speed and torque thresholdωT_(threshold) (ω_(motor)*T<ωT_(threshold)).
 16. The power toolaccording to claim 7, wherein said at least one control unit isconfigured to provide said step-up converter with a step-upenabling/disabling signal S_(step-up_on/off), said step-up converterbeing configured to enable or disable the voltage conversion of saidstep-up converter based on said step-up enabling/disabling signalS_(step-up_on/off); and wherein said at least one control unit isconfigured to base said step-up enabling/disabling signalS_(step-up_on/off) and/or said bypass enabling/disabling signalS_(bypass_on/off) on a relation between said output power P_(output)being provided to said electrical motor unit and a power thresholdP_(threshold).
 17. The power tool according to claim 16, wherein said atleast one control unit is configured to generate a step-up enablingsignal S_(step-up_on) and a bypass disabling signal S_(bypass_off) whensaid output power P_(output) is lower than said power thresholdP_(threshold) (P_(output)<P_(threshold)).
 18. The power tool accordingto claim 7, wherein said at least one control unit is configured toprovide said step-up converter with a step-up enabling/disabling signalS_(step-up_on/off), said step-up converter being configured to enable ordisable the voltage conversion of said step-up converter based on saidstep-up enabling/disabling signal S_(step-up_on/off); and wherein saidbypass enabling/disabling signal S_(bypass_on/off) and said step-upenabling/disabling signal S_(step-up_on/off) are complementary signals.19. The power tool according to claim 1, wherein said step-up converterincludes two step-up transistor circuits being operated in mutuallyopposite phases.
 20. The power tool according to claim 1, wherein saidstep-up converter and said bypass circuit are arranged integrated withina body of said power tool, said step-up converter and said bypasscircuit being connected to said electrical motor unit and beingconnectable to said battery unit.
 21. The power tool according to claim1, wherein said step-up converter and said bypass circuit are arrangedintegrated with and connected to said battery unit, and are connectableto said electrical motor unit.
 22. The power tool according to claim 1,wherein said step-up converter and said bypass circuit are arrangedseparately between said battery unit and said electrical motor unit,said step-up converter and said bypass circuit being connectable to saidbattery unit and to said electrical motor unit.
 23. The power toolaccording to claim 1, wherein said battery unit includes at least onesuper capacitor.
 24. The power tool according to claim 1, wherein saidpower tool includes a brake chopper arranged for consuming energyprovided by said electrical motor unit when said rotational speed ofsaid electrical motor unit is reduced.
 25. A method for providing anelectrical motor unit of a power tool with an output voltage U_(output),the method comprising: converting, when a step-up converter that isconnectable between a battery unit and said electrical motor unit isenabled, a battery voltage U_(battery) that is provided to said step-upconverter by said battery unit to a higher step-up voltage U_(step-up),U_(step-up)>U_(battery), and providing said step-up voltage U_(step-up)to said electrical motor unit as said output voltage U_(output),U_(output)=U_(step-up); connecting, when a bypass circuit that isarranged in parallel with said step-up converter is enabled, saidbattery unit to said electrical motor unit, and providing said batteryvoltage U_(battery) to said electrical motor unit as said output voltageU_(output), U_(output)=U_(battery); and controlling, by use of at leastone control unit, said step-up converter and said bypass circuit suchthat said output voltage U_(output) is switchable between said batteryvoltage U_(battery) and said step-up voltage U_(step-up), to alter saidoutput voltage U_(output) that is provided to said electrical motor unitto achieve a higher rotational speed of said electrical motor unit and alower torque provided by said power tool during a first phase of a screwtightening process, followed by a lower rotational speed of saidelectrical motor unit and a higher torque provided by said power toolduring a second phase of the screw tightening process; wherein thecontrolling of said step-up converter and said bypass circuit isperformed based on at least one of a plurality of different tool relatedparameters, said parameters comprising (i) said output voltageU_(output), (ii) an output current I_(output) being provided to saidelectrical motor unit, (iii) said rotational speed ω_(motor) of saidelectrical motor unit multiplied with said torque T being provided bysaid tool, ω_(motor)*T, and (iv) an output power P_(output) beingprovided to said electrical motor unit.
 26. The method according toclaim 25, wherein said at least one control unit disables said step-upconverter and enables said bypass circuit when the at least one of saidparameters (U_(output), I_(output), ω_(motor)*T, P_(output)) reachesabove or below a certain threshold (U_(threshold), I_(threshold),ωT_(threshold), P_(threshold)) relating to the at least one of saidparameters.
 27. The method according to claim 25, wherein said at leastone control unit disables said step-up converter and enables said bypasscircuit when said output voltage U_(output) is lower than a voltagethreshold U_(threshold) (U_(output)<U_(threshold)).
 28. The methodaccording to claim 25, wherein said at least one control unit disablessaid step-up converter and enables said bypass circuit when said outputcurrent I_(output) is higher than or equal to a current thresholdI_(threshold) (I_(output)≥I_(threshold)).
 29. The method according toclaim 25, wherein said at least one control unit enables said step-upconverter and disables said bypass circuit when said rotational speedω_(motor) of said electrical motor unit multiplied with said torque Tthat is provided by said power tool, ω_(motor)*T, is lower than a speedand torque threshold ωT_(threshold) (ω_(motor)*T<ωT_(threshold)). 30.The method according to claim 25, wherein said at least one control unitenables said step-up converter and disables said bypass circuit whensaid output power P_(output) that is provided to said electrical motorunit is lower than a power threshold P_(threshold)(P_(output)<P_(threshold)).
 31. The method according to claim 25,wherein said screw tightening process includes: enabling said step-upconverter and disabling said bypass circuit during said first phase ofsaid screw tightening process, thereby providing said step-up voltageU_(step-up) to said electrical motor unit as said output voltageU_(output), U_(output)=U_(step-up), whereby said rotational speedω_(motor) of said electrical motor unit is increased as a result of thehigher step-up voltage U_(step-up); and enabling said bypass circuit anddisabling said step-up converter during said second phase of said screwtightening process, thereby providing said battery voltage U_(battery)to said electrical motor unit as said output voltage U_(output),U_(output)=U_(battery), whereby said rotational speed ω_(motor) of saidelectrical motor unit is decreased as a result of the lower batteryvoltage U_(battery).
 32. A non-transitory computer readable mediumstoring a computer program that is executable by a computer of a powertool to perform the method according to claim 25.